The salinity of the open ocean is quite stable in any given area, but the salinity of shallow inshore waters can fluctuate considerably in some areas, due primarily to influx of fresh water into the system, and to a lesser extent, evaporation of fresh water from the system. Coastal areas near river mouths are apt to have lower salinity then those more distant from major fresh water sources. Areas north or south (east or west) of the fresh water source may be affected differently, depending on the direction of prevailing currents in the area. Also, surface salinity will be temporarily lower after a heavy rainfall, due to both direct rainfall onto the ocean, and increased runoff from the land. Salinity in sheltered bays, inlets, salt ponds, etc. is often higher than in the nearby ocean, especially during hot summer weather conditions, due to evaporation of water from the system. This is true even in very large enclosed bodies of salt water, such as the Mediterranen Sea and the Red Sea, which have a higher salinity than the adjoining ocean waters. Open ocean salinity ranges from about 32 to 37 grams of dissolved salts per kilogram of water. Some average open ocean salinities for broad geographic areas are: Arctic Ocean: 32-33 g/kg At the equator: 35 g/kg North Pacific: 34.5 g/kg South Pacific: 35.5 g/kg Indian Ocean: 35.5 g/kg Sargasso Sea: 36.5-37 g/kg North Atlantic (North Sea): 34 g/kg South Atlantic: 36-37 g/kg Gulf of Mexico: 36-37 g/kg Mediterranean Sea: 37-39 g/kg Red Sea: 38-41 g/kg (these values are taken from the Biological Data Book of the Federation of American Societies For Experimental Biology) Paul M.